Add missing test coverage for azuremachine_validation.go

[willie-yao]

/kind cleanup

Describe the solution you'd like Currently, azuremachine_validation.go is missing unit tests in the following areas:

• ValidateDataDisks and validateManagedDisksUpdate
  • Add the following test cases to TestAzureMachine_ValidateDataDisks
    • disk.Lun = nil
    • disk.Lun < 0 || disk.Lun > 63
    • oldDisk.ManagedDisk.DiskEncryptionSet != nil && newDisk.ManagedDisk.DiskEncryptionSet != nil
    • (newDiskParams.DiskEncryptionSet != nil && oldDiskParams.DiskEncryptionSet == nil) || (newDiskParams.DiskEncryptionSet == nil && oldDiskParams.DiskEncryptionSet != nil)
• ValidateDataDisksUpdate
  • Add the following test cases to TestAzureMachine_ValidateDataDisksUpdate
    • (newDisk.Lun != nil && oldDisk.Lun != nil) && (newDisk.Lun != oldDisk.Lun)
    • Both newDisk.Lun and oldDisk.Lun are nil
    • Both newDisk.Lun and oldDisk.Lun are non nil but are equal to each other
• ValidateDiagnostics
  • Create a new unit test for this function.

Environment:

• cluster-api-provider-azure version:
• Kubernetes version: (use kubectl version):
• OS (e.g. from /etc/os-release):

[willie-yao]

/help /kind cleanup /remove-kind feature

[k8s-ci-robot]

@willie-yao: This request has been marked as needing help from a contributor.

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In response to [this](https://github.com/kubernetes-sigs/cluster-api-provider-azure/issues/3374): >/help >/kind cleanup >/remove-kind feature Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes/test-infra](https://github.com/kubernetes/test-infra/issues/new?title=Prow%20issue:) repository.

[khareyash05]

/assign